1. Field of the Invention
The present invention relates to focal plane shutters.
2. Description of the Related Art
Conventionally, a focal plane shutter includes: leading blades; trailing blades; a driving arm coupled to them, and a drive member coupled to the drive arm (see Japanese Unexamined Patent Application Publication No. 2002-296641). The drive member is swingably supported about a given position. In response to the swinging of the drive member, the drive arm is driven, and then the reading or trailing blades are driven. This drive member (drive lever) is operated by an urging force of a drive spring. One end of the drive spring is engaged with the drive member. Also, the focal plane shutter is provided with an adjustment mechanism for adjusting the urging force of the drive spring. This adjustment mechanism includes: a ratchet wheel that engages the other end of the drive spring; and a ratchet pawl that abuts the ratchet wheel to define a rotational direction and a stop position of the ratchet wheel. The ratchet wheel and the drive spring are concentrically arranged about a given axis. The urging force of the drive spring can be adjusted by the ratchet wheel, and the ratchet pawl can stop the ratchet wheel at a given position. Thus, the shutter speed can be adjusted.
In the assembling processes of the adjustment mechanism as mentioned above, the drive spring is concentrically arranged with a spindle provided to stand on the board, and then the ratchet wheel is arranged above the drive spring. Next, a printed substrate assembled with the ratchet pawl is attached on an upper end portion of the spindle. In this time, since the ratchet pawl is assembled into the ratchet wheel from its upper side in its axis direction, the ratchet pawl and the periphery of the ratchet wheel are abutted in this assembling process. This abutment may cause the ratchet pawl to chip the peripheral surface of the ratchet wheel, and thus the chips may be generated. Such chips adhere to the periphery of a mechanism for driving the leading and trailing blade, thereby influencing the shutter operation. Further, the chips generated in this way may adhere to an inside of the shutter, and are then discharged from the inside of the shutter after the shutter is installed into a camera body, and the chips may adhere to a lens surface or an image pickup element, whereby the image quality may be degraded.